1. Field of the Invention
This invention relates to a shifting mechanism for various movable mirrors used within a photographic camera and more particularly to a lifting mechanism, for example, for a main movable mirror which is arranged to be shiftable into a photo-taking optical path provided between a photo-taking lens and a film surface within a single-lens reflex camera and to be retractable from the optical path.
2. Description of the Prior Art
Various movable mirrors are arranged within a photographic camera. The main movable mirror of a single-lens reflex camera, for example, is arranged to be retractable by lifting it from its original position within a photo-taking optical path during a photographic operation and to be returned to the original position by means of a return spring upon completion of the photographic operation. However, both the main movable mirror and a stopper for receiving the mirror at its original position are resilient. It has been, therefore, difficult to prevent the main movable mirror from rebounding on its return due to the force of inertia of the mirror after its collision against the stopper.
The rebound of a movable mirror which takes place on its return to its original position has presented various problems. For example, in a case where a main movable mirror is provided for image observation at a view finder or for light measurement, the view finder image blurs during the rebound of the mirror. This not only prevents clear observation of the image but also makes it impossible to obtain an adequate photograph in the event of a high speed continuous automatic photographing operation to be carried out with an automatic film winder. In carrying out a high speed continuous automatic photographing operation with an automatic winder, it is necessary to perform light measurement and to determine exposure conditions within a short film winding time. However, the rebound of the main movable mirror which reflects part of or most of the light coming from an object through a photo-taking lens during the process of light measurement, prevents the light from reaching to a light receiving photo-sensitive element provided for TTL light measurement. In that event, a proper exposure setting is impaired. In a case where an auxiliary movable mirror is provided for the purpose of detecting a focus condition of the camera for automatic focusing, a high speed continuous automatic focusing photographing operation also calls for quick detection and quick focus adjustment within a short film winding time. In such a case, rebound of the above-stated auxiliary movable mirror which is provided for detecting a focus condition not only causes a blur of the object image on the focus detecting photo-sensitive element but also brings forth an erroneous focus condition signal as a result of a change caused thereby in the length of an optical path between the photo-taking lens and the photo-sensitive element.
To prevent the rebound of a movable mirror which takes place on its return to its original position, the present applicant has previously proposed a method disclosed in U.S. Pat. No. 4,327,982. In accordance with this method, an antibouncer member which is always disposed within the turning locus of the movable mirror is arranged to be brought by a spring force into sliding contact with a member attached to the movable mirror when the movable mirror comes to a point in the neighbourhood of its original position. This arrangement, however, inevitably causes the antibouncer member to become an extra load when the movable mirror is to be lifted. This load presents another problem. To effectively suppress the rebound of the movable mirror which takes place on its return to an original position, the spring force for the sliding contact must be increased. Then, the increased spring force results in an excessive load for the mirror lifting operation. Thus, the method presents a contradictory problem.